Memory is one type of integrated circuitry and is used in computer systems for storing data. Memory may be fabricated in one or more arrays of individual memory cells. Memory cells may be written to, or read from, using digit lines (which may also be referred to as bit lines, data lines, or sense lines) and access lines (which may also be referred to as word lines). The digit lines may conductively interconnect memory cells along columns of the array, and the access lines may conductively interconnect memory cells along rows of the array. Each memory cell may be uniquely addressed through the combination of a digit line and an access line.
Memory cells may be volatile, semi-volatile, or non-volatile. Non-volatile memory cells can store data for extended periods of time in the absence of power. Non-volatile memory is conventionally specified to be memory having a retention time of at least about 10 years. Volatile memory dissipates and is therefore refreshed/rewritten to maintain data storage. Volatile memory may have a retention time of milliseconds or less. Regardless, memory cells are configured to retain or store memory in at least two different selectable states. In a binary system, the states are considered as either a “0” or a “1”. In other systems, at least some individual memory cells may be configured to store more than two levels or states of information.
A field effect transistor is one type of electronic component that may be used in a memory cell. These transistors comprise a pair of source/drain regions having a semiconductive channel region there-between. A conductive gate is adjacent the channel region and separated there-from by a thin gate insulator. Application of a suitable voltage to the gate allows current to flow from one of the source/drain regions to the other through the channel region. When the voltage is removed from the gate, current is largely prevented from flowing through the channel region. Field effect transistors may also include additional structure, for example a reversibly programmable charge-storage region as part of the gate construction between the gate insulator and the conductive gate. Field effect transistors may be ferroelectric wherein at least some portion of the gate construction (e.g., the gate insulator) comprises ferroelectric material. Two different polarized states of the ferroelectric material in transistors may be characterized by different threshold voltage (Vt) for the transistor or by different channel conductivity for a selected operating voltage.
One type of transistor is a fin field effect transistor (finFET). Each finFET includes a fin (a tall thin semiconductor member) typically extending generally perpendicularly from a substrate. The fin comprises a pair of opposing sidewalls, and gate material is provided along at least one of the sidewalls. The gate material is spaced from the sidewalls by gate insulator material. A pair of source/drain regions is provided within the fin, and a channel region extends between the source/drain regions. In operation, the gate is used to selectively control current flow within the channel region. The finFETs may be used as access transistors in integrated memory arrays, such as, for example, dynamic random access memory (DRAM) arrays. In some applications, finFETs have their source/drain regions on a pair of upwardly-projecting pedestals, and the channel region is along a trough or valley extending between the pedestals. A charge-storage device (for instance, a capacitor) is electrically coupled to one of the source/drain regions, and a sense line is electrically coupled to the other of the source/drain regions. The gate is beneath the source/drain regions, and extends along the valley comprising the channel region. As memory cell size has decreased and density has increased, it has become more difficult to align the charge-storage device with the targeted source/drain regions to which such electrically couple.